Pharmaceutical preparations for oral administration are generally intended to have the drug disintegrated in the stomach, etc. to insure that its efficacy is exhibited as quickly as possible. Thus, little R&D efforts have so far been directed to pharmaceutical preparations for oral administration that are so adapted as to release the drug only at specific sites in the intestines. Even if L-ascorbic acid containing preparations are administered orally with a view to delivering the drug to the large intestine so that it is released there, the drug is decomposed in the stomach and mostly absorbed by the small intestine, with little being delivered to the large intestine.
Sustained-release preparations have been developed as pharmaceuticals that are administered once or twice a day and which yet are capable of maintaining the blood concentration of the drug beyond a certain level over a prolonged time. However, even such sustained-release preparations are incapable of permitting the drug to be released only at desired sites in the intestines. For instance, even if it is intended to have the drug absorbed by the large intestine, part of the drug will be released before it reaches the large intestine since it takes 4-5 hours for the administered drug to reach the large intestine during a fasting period. Further, the drug reaching the large intestine is released only slowly so that the percent absorption of the drug is too low to insure efficient administration of the drug. Besides sustained-release preparations, administration can be made through the rectum either in the form of suppositories or by means of enema but even these methods are incapable of delivering the drug effectively to every part of the large intestine. Hence, heretofore, no means have been available by which salazosulfapyridine and prednisolone which are therapeutics for ulcerous colitis can be efficiently administered to reach appropriate sites in the large intestine.